Sewing method and device

ABSTRACT

A sewing mechanism is provided with: a post bed and sewing needles, wherein an article to be sewn is interposed between the post bed and the sewing needles. When the post bed comes closer to the article to be sewn than that in the previous sewing by at least a predetermined distance, in other words, when a separation distance between the article to be sewn and the post bed becomes less than that in the previous sewing by at least a predetermined distance, a thread pulling mechanism pulls threads hooked in needle holes of the sewing needles in a direction away from the post bed.

TECHNICAL FIELD

The present invention relates to a sewing method for forming stitches in an article to be sewn with a needle and a looper, and to a device for the same.

BACKGROUND ART

In order to create a sense of luxury in the cabin of an automobile, stitching patterns may be sewn (stitched) in a skin material that has been cut or molded to match the shape of an interior base material of an instrument panel. Recently, attempts have been made to perform this sewing with a sewing robot having a sewing machine, which is a sewing mechanism, provided on a tip arm thereof.

When performing the sewing, it is possible for uneven sewing to occur. In order to eliminate such problems, JP H08-266765 A and JP 2001-038084 A propose a sewing device (sewing machine) capable of changing the tension on a thread hooked on a needle.

SUMMARY OF THE INVENTION

Many interior base materials have curved surfaces, corners (bent portions), and the like. In order to sew on an interior base material and a skin material (article to be sewn) having such a complicated shape, the needle may be moved from a flat portion to another flat portion via a bent portion, for example. In such a process, each arm of the sewing robot operates suitably to keep the needle constantly facing a post bed through the article to be sewn. During this, in accordance with the change in the posture of the post bed, the relative separation distance between the article to be sewn and the post bed changes. Specifically, the interior base material and post bed become relatively closer to each other along the flat portions, but become relatively farther from each other along the bent portions.

When sewing along a flat portion where the article to be sewn and the post bed are close to each other, the length of the thread between the needle or article to be sewn and the post bed becomes small. On the other hand, when sewing along a bent portion where the article to be sewn and the post bed are far from each other, the length of the thread between the needle or article to be sewn and the post bed becomes large. Accordingly, when sewing along the flat portion after finishing sewing along the bent portion, the thread becomes loose. In this case, the stitches may not be formed and stitching defects such as fraying may occur. Furthermore, if sewing continues in this state, it is possible for the thread to become unable to pass through the loop portion formed by the previous sewing, for example.

On the other hand, when sewing along the bent portion after finishing sewing along the flat portion, the thread is pulled. In this case, the aesthetics of the seam may be spoiled due to the thread biting into the article to be sewn.

The prior art disclosed in JP H08-266765 A and JP 2001-038084 A is for adjusting the thread tension with a typical fixed sewing machine that performs sewing in a state where the positions of the thread and looper are fixed, and cannot eliminate loosening of the thread when the relative separation distance between the article to be sewn and the post bed changes. In other words, in the prior art, a problem has become apparent that the looseness or tension of the thread cannot be eliminated in a movable sewing device in which the thread and the looper move.

The present invention has a main object of providing a sewing method making it possible to eliminate thread looseness or tension and to realize aesthetically beautiful stitching.

The present invention has another object of providing a sewing device configured to be capable of performing the sewing method described above.

According to one embodiment of the present invention, provided is a sewing method for forming stitches on an article to be sewn, using a needle configured to pierce or withdraw from the article to be sewn in accordance with repetition of back and forth movement, and a looper that faces the needle with the article to be sewn therebetween and is housed inside a post bed, the sewing method comprising: when the post bed has become closer to the article to be sewn by at least a prescribed amount than in immediately preceding sewing, pulling a thread hooked on the needle in a direction away from the post bed, or, when the post bed has become farther from the article to be sewn by at least a prescribed amount than in the immediately preceding sewing, pulling the thread hooked on the needle in a direction toward the post bed.

According to another embodiment of the present invention, provided is a sewing device for forming stitches on an article to be sewn, using a needle configured to pierce or withdraw from the article to be sewn in accordance with repetition of back and forth movement, and a looper that faces the needle with the article to be sewn therebetween and is housed inside a post bed, the sewing device comprising: a thread pulling mechanism configured to pull a thread, which has been hooked on the needle, in a direction away from or toward the post bed; and a control section configured to perform control to operate the thread pulling mechanism when a distance between the post bed and the article to be sewn differs by at least a prescribed amount from a distance in immediately preceding sewing.

When the post bed has become closer to the article to be sewn by at least a prescribed amount than in immediately preceding sewing, that is, when the separation distance between the article to be sewn and the post bed has become smaller by at least the prescribed amount than in the immediately preceding sewing, the thread becomes loose based on this difference in the separation distance. Therefore, with the present invention, the thread is pulled by the thread pulling mechanism at this time in a direction away from the post bed. As a result, the looseness of the thread is eliminated, and therefore, when the needle pierces the article to be sewn, the needle can pass through the loop portion formed by the previous sewing, for example.

On the other hand, when the post bed has become farther from the article to be sewn by at least a prescribed amount than in the immediately preceding sewing (when the separation distance between the article to be sewn and the post bed has become greater by at least the prescribed amount than in the immediately preceding sewing), the thread becomes tense. In this case, the thread is pulled by the thread pulling mechanism in a direction toward the post bed. As a result, the thread tension is eliminated, and therefore the thread can be prevented from biting into the article to be sewn.

In this way, according to the present invention, when a separation distance between the post bed and the article to be sewn differs by at least a prescribed amount from the distance in the immediately preceding sewing, the thread is pulled in a direction toward or away from the post bed, and therefore it is possible to form aesthetically beautiful stitching.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configurational diagram of a sewing device according to an embodiment of the present invention;

FIG. 2 is a schematic perspective view showing specific examples of an article to be sewn that is to be sewn by the sewing device of FIG. 1, and seating portions used in this sewing;

FIG. 3 is an enlarged perspective view of essential parts in a sewing mechanism and the seating portions of the sewing device of FIG. 1;

FIG. 4 is a schematic perspective view of essential parts showing two loopers housed inside a post bed;

FIG. 5 is a schematic front view of a casing that forms the sewing device of FIG. 1;

FIG. 6 is an enlarged side view of essential parts showing a state in which needles have entered inside the post bed and threads have been hooked onto hooking claws of the loopers;

FIG. 7 is a schematic perspective view of essential parts showing a state in which loop portions, which are formed by the needles and the loopers of FIG. 4, are joined together;

FIG. 8 is a schematic flow showing the posture change when the post bed moves from a flat portion to a bent portion;

FIG. 9 is a schematic front view of essential parts showing a state in which the threads have been pulled by the thread pulling mechanism; and

FIG. 10 is a schematic front view of a casing provided with a thread pulling mechanism differing from that of FIG. 5.

DESCRIPTION OF THE INVENTION

Preferred embodiments of a sewing method according to the present invention will be presented and described in detail below with reference to the accompanying drawings in connection with a sewing device for implementing the sewing method. In the following description, the terms “up”, “down”, “left”, and “right” corresponds to upward, downward, leftward, and rightward in each drawing, but these directions are merely shown for convenience in order to facilitate understanding, and do not define the directions when actually using the sewing device.

FIG. 1 is a schematic configurational diagram of a sewing device 10 according to the present embodiment. This sewing device 10 includes a holding mechanism 12, a sewing mechanism 14, and a sewing robot 16 serving as a transport mechanism that transports the sewing mechanism 14. The sewing mechanism 14 is attached to a tip arm 18 of the sewing robot 16 formed by an articulated robot.

First, a general description of the holding mechanism 12 is provided. The holding mechanism 12 includes a frame 20, a plurality of retracting mechanisms 22 that are supported on the frame 20, and a seating portion 24 provided in each of the retracting mechanisms 22. The frame 20 includes a base plate 28 shaped as a substantially flat plate. A retraction air cylinder 30 forming the retracting mechanism 22 is erected on the base plate 28. Specifically, the retraction air cylinder 30 is supported on the frame 20 in a posture whereby a reciprocation rod 32 faces upward in FIG. 1.

The retracting mechanism 22 includes, in addition to the retraction air cylinder 30, a guide bush 34 and a guide pin 36. The guide bush 34 is fixed near the top end of the frame 20, and a tip of the reciprocation rod 32 is inserted therein in a slidable manner. The bottom end of the guide pin 36 is connected to the top end of the reciprocation rod 32 inside the guide bush 34.

The seating portion 24 is provided at the top end of the guide pin 36. Accordingly, the guide pin 36 and the seating portion 24 move back and forth integrally with the reciprocation rod 32. In other words, each seating portion 24 is capable of moving forward or backward (retracting) individually under the effect of the retracting mechanism 22 in which the seating portion 24 is provided. In FIG. 1, the forward motion corresponds to rising and the backward motion corresponds to lowering.

The plurality of seating portions 24 are arranged in parallel in a sewing direction in which the sewing mechanism 14 performs sewing, that is, along a sewing line L shown in FIG. 2. Seating surfaces 37, which are the top surfaces of the seating portions 24, are provided along the sewing line L and curved with a curvature radius substantially equivalent to the curvature radius of an article to be sewn 100 along the sewing line L. If the article to be sewn 100 is an interior base material 102 and a skin material 104 of an instrument panel, for example, the seating portions 24 are arranged as shown by the dashed lines in FIG. 2. The seating portions 24 sequentially retract as the sewing mechanism 14 approaches, as described further below.

The seating surfaces 37 are formed to have substantially the same shape as the article to be sewn 100, as described above (see FIG. 2 or FIG. 3). As a result, the shape of the article to be sewn 100 placed on the seating surfaces 37 is preserved.

As shown in FIGS. 1 and 3, a plurality of suction holes 38 are formed in each seating portion 24. These suction holes 38 are in communication with a suction pump (not shown in the drawings) via negative pressure flow paths and exhaust pipes 40 inside the seating portions 24. By creating suction via the suction holes 38 under the effect of the suction pump, the seating portions 24 hold by suction the article to be sewn 100 placed on the seating portions 24.

The sewing mechanism 14 includes a casing 50 formed with a lying U shape in a side view. The tip arm 18 of the sewing robot 16 is connected to the front surface of a vertical pillar portion 52 forming this casing 50. Furthermore, a sewing motor 54 is provided on one side surface of the vertical pillar portion 52.

The casing 50 further includes a first lateral pillar portion 56 and a second lateral pillar portion 58 that face each other and extend in the same direction respectively from the bottom end and the top end of the vertical pillar portion 52. The first lateral pillar portion 56, which is on the bottom, is provided with a post bed 60 that extends toward the second lateral pillar portion 58, which is on the top. As shown in detail in FIG. 4, a first looper 62 a and a second looper 62 b are housed inside the post bed 60. A driven gear 66 is interposed between the first looper 62 a and the second looper 62 b. This driven gear 66 forms a drive mechanism together with a rotating shaft of the sewing motor 54 via a timing belt, gear train, or the like inside the casing 50. Accordingly, when the rotating shaft of the sewing motor 54 rotates, the driven gear 66 rotates in a following manner, and the first looper 62 a and the second looper 62 b rotate integrally with this following rotation. The configuration described above is widely known, and therefore detailed drawings and descriptions thereof are omitted.

The first looper 62 a and the second looper 62 b each include a hook-shaped hooking claw 70. The hooking claws 70 respectively hook threads 74 a and 74 b, which pass through respective needle eyes 73 (see FIG. 6) of a first sewing needle 72 a and a second sewing needle 72 b. The top end surface of the post bed 60 is open, and therefore the first sewing needle 72 a and the second sewing needle 72 b can be inserted into or withdrawn from the inside of the post bed 60.

The second lateral pillar portion 58 (see FIG. 1) is provided with a reciprocating hilt 78 that moves back and forth in a manner to move toward and away from the first lateral pillar portion 56. The reciprocating hilt 78 is provided with both the first sewing needle 72 a and the second sewing needle 72 b (both of which are needles) via a needle holder 79. The first sewing needle 72 a and the second sewing needle 72 b move back and forth integrally with the reciprocating hilt 78, in accordance with the rotation of the rotating shaft of the sewing motor 54. Since this configuration is also widely known, detailed drawings and descriptions thereof are omitted. The first sewing needle 72 a and the second sewing needle 72 b respectively face the first looper 62 a and the second looper 62 b in the post bed 60 (see FIG. 4).

The back and forth movements of the first sewing needle 72 a and the second sewing needle 72 b trace elliptical trajectories, when viewed from the front surface of the casing 50. As a result, even when the casing 50 is moved at a constant speed, the first sewing needle 72 a and the second sewing needle 72 b pierce the article to be sewn 100 while maintaining certain positions relative to the article to be sewn 100.

The needle eyes 73 are formed penetrating respectively through the tips of the first sewing needle 72 a and the second sewing needle 72 b. The threads 74 a and 74 b for forming parallel stitches 112 (see FIG. 2), which are a seam, are drawn out from a thread supplying section such as a bobbin (not shown in the drawings), and the tips of these threads 74 a and 74 b are passed through the needle eyes 73.

As shown in FIG. 5, a thread pushing air cylinder 80 (pushing mechanism), which serves as a thread pulling mechanism, is provided on the second lateral pillar portion 58. The thread pushing air cylinder 80 includes a thread pushing rod 84 having a thread passing groove 82 formed on the bottom end surface thereof. After having passed through the thread passing groove 82, the threads 74 a and 74 b drawn out from the thread supplying section are hooked onto the respective needle eyes 73 of the first sewing needle 72 a and the second sewing needle 72 b. Accordingly, when the thread pushing rod 84 moves forward (corresponding to lowering in FIGS. 1 and 5), the threads 74 a and 74 b are pushed to be pulled toward the thread supplying section side. In other words, at this time, the threads 74 a and 74 b are pulled in a direction away from the post bed 60. The second lateral pillar portion 58 is provided with a tab portion 86, and the threads 74 a and 74 b are inserted through a thread insertion hole (not shown in the drawings) formed in this tab portion 86.

In the above configuration, the holding mechanism 12, the sewing mechanism 14, and the sewing robot 16 are electrically connected to a control section 90, which is a control means. The sewing robot 16 moves the sewing mechanism 14 at a constant speed along the sewing line L (see FIG. 2), under the control of the control section 90. Furthermore, at this time, the posture of the casing 50 is changed to match the shape of the article to be sewn 100 at the sewing position, thereby adjusting the posture of the sewing mechanism 14 such that the first sewing needle 72 a and the second sewing needle 72 b become substantially perpendicular to the sewing position on the article to be sewn 100.

The control section 90 also controls the activating or deactivating of the sewing motor 54 and the activating or deactivating of the thread pushing air cylinder 80.

The sewing device 10 according to the present embodiment is basically configured as described above, and the following is a description of the operational effects thereof in relation to the sewing method according to the present embodiment.

When sewing is performed on the article to be sewn 100, first, as shown in FIGS. 2 and 3, the article to be sewn 100 is placed on the seating portions 24 of the holding mechanism 12, and the suction pump is activated. Consequently, suction is exerted via the suction holes 38, and as a result, the article to be sewn 100 placed on the seating portions 24 is sucked and held in a state of being seated on the seating surfaces 37.

Next, the sewing robot 16 operates suitably under the control of the control section 90 to bring the tip arm 18 near the article to be sewn 100 and, as shown in FIG. 3, position the article to be sewn 100 in a manner to be sandwiched between the post bed 60 (first looper 62 a and second looper 62 b), and the first sewing needle 72 a and the second sewing needle 72 b. In other words, the first looper 62 a and the second looper 62 b, and the first sewing needle 72 a and the second sewing needle 72 b face each other with the article to be sewn 100 therebetween. In this way, by providing the sewing robot 16 that transports the sewing mechanism 14, it becomes easy to transport the sewing mechanism 14 to the vicinity of the article to be sewn 100. After the threads 74 a and 74 b have been drawn out from the thread supplying section and passed through the thread passing groove 82 formed in the thread pushing rod 84, which forms the thread pushing air cylinder 80, these threads 74 a and 74 b are passed separately through the respective needle eyes 73 of the first sewing needle 72 a and the second sewing needle 72 b.

In FIG. 3 (and the enlarged portion of FIG. 2), a state occurring while the sewing progresses from left to right is shown. As can be understood from FIG. 3, when the post bed 60, the first sewing needle 72 a, and the second sewing needle 72 b reach a location where sewing is performed, the retraction air cylinder 30 forming the retracting mechanism 22 retracts the reciprocation rod 32 and the guide pin 36 to move the seating portion 24 away from the article to be sewn 100. When this retraction occurs, the guide bush 34 guides the reciprocation rod 32 and the guide pin 36.

In accordance with the seating portion 24 moving away from the article to be sewn 100, a clearance occurs between the seating portion 24 and the article to be sewn 100. The post bed 60 enters this clearance. In this way, the sewing device 10 is configured to sequentially retract the seating portions 24 according to the position of the sewing mechanism 14, thereby arranging the post bed 60 on the back side of the article to be sewn 100, and perform sewing. The suction from the suction holes 38 of the seating portion 24 to be retracted is stopped before this retraction.

In a case where the article to be sewn 100 is an instrument panel, the interior base material 102 forming this instrument panel exhibits relatively high rigidity. Therefore, even when the seating portion 24 is moved away from a portion of the instrument panel, the instrument panel does not experience deformation such as warping at this location.

Next, the control section 90 activates the sewing motor 54. As a result, the reciprocating hilt 78 performs back and forth movement in the up-down direction. Obviously, the first sewing needle 72 a and the second sewing needle 72 b held by the needle holder 79 also move back and forth in the up-down direction, integrally with the reciprocating hilt 78. On the other hand, the driven gear 66 (see FIG. 4) rotates in a following manner, and the first looper 62 a and the second looper 62 b rotate integrally and in synchronization with the driven gear 66. The first looper 62 a and the second looper 62 b rotate one time while the first sewing needle 72 a and the second sewing needle 72 b move back and forth one time.

While travelling along the outbound path downward from the back end (top dead center), the first sewing needle 72 a and the second sewing needle 72 b pierce the article to be sewn 100 from the top end surface side thereof as shown in FIG. 6, and when reaching the forward end (bottom dead center), the tips of the first sewing needle 72 a and the second sewing needle 72 b protrude from the bottom end surface of the article to be sewn 100 and enter the empty space inside the post bed 60. In accordance with this, the threads 74 a and 74 b penetrate through the article to be sewn 100. After this, the first sewing needle 72 a and the second sewing needle 72 b travel on the return path from the bottom dead center to the top dead center, and are withdrawn from the post bed 60 and the article to be sewn 100 during this travel.

When the threads 74 a and 74 b have penetrated through the article to be sewn 100, the respective hooking claws 70 of the first looper 62 a and the second looper 62 b reach the top dead center. The threads 74 a and 74 b that have penetrated through the article to be sewn 100 are hooked on the hooking claws 70, and are pulled downward in FIGS. 2 and 3 in accordance with the rotation of the first looper 62 a and the second looper 62 b to form loop portions 110 shown in FIG. 7 on the bottom end surface side of the article to be sewn 100. The regions of the threads 74 a and 74 b pulled the next time the first sewing needle 72 a and the second sewing needle 72 b pierce the article to be sewn 100 (the next time the first looper 62 a and the second looper 62 b rotate) are inserted into the loop portions 110.

The sewing robot 16 operates suitably to move the sewing mechanism 14 parallel to the article to be sewn 100. By repeating the back and forth movement of the first sewing needle 72 a and the second sewing needle 72 b and the rotation of the first looper 62 a and the second looper 62 b at the same time as this parallel movement, the loop portions 110 are joined to each other to realize the sewing. FIG. 7 shows an example of only the thread 74 a, but it is obvious that the loop portions 110 are joined to each other in the same manner for the thread 74 b as well. On the other hand, the parallel stitches 112 connected linearly are formed on the top end surface side of the article to be sewn 100, as shown in FIG. 2.

The sewing mechanism 14 is moved at a constant speed to the right in FIGS. 2 and 3, for example, by the sewing robot 16. In accordance with this, the seating portion 24 at a position interfering with the sewing mechanism 14 retracts from the article to be sewn 100 due to the effect of the retracting mechanism 22. In other words, after the suction from the suction holes 38 has been stopped, the reciprocation rod 32 is lowered such that the seating portion 24 is retracted to a position where the seating portion 24 does not interfere with the sewing mechanism 14. Furthermore, at a location where the sewing has ended and the sewing mechanism 14 has moved away, suction from the suction holes 38 is resumed, and the reciprocation rod 32 and the guide pin 36 rise up while being guided by the guide bush 34 due to the effect of the retracting mechanism 22. As a result, the article to be sewn 100 becomes placed on the seating portions 24.

Here, in a case where the article to be sewn 100 is an instrument panel with a shape such as shown in FIG. 2, flat portions, such as a high flat portion 120 and a low flat portion 122, and bent portions 124, such as a curved portion and a folded portion, are usually formed in the article to be sewn 100. As shown in FIG. 8, when moving from the flat portion (high flat portion 120, low flat portion 122, or the like) to the bent portion 124, the post bed 60 changes its posture. This is because the sewing robot 16 (see FIG. 1), in accordance with teaching implemented in advance, changes the posture of the sewing mechanism 14 such that the post bed 60 and the first sewing needle 72 a and the second sewing needle 72 b become substantially perpendicular to the surface of the portion being sewed.

At the high flat portion 120 and the low flat portion 122, that is, a flat portion where there is almost no height difference, the post bed 60 contacts or is separated from the back surface of the article to be sewn 100 by only a slight distance, as shown in the enlarged portion of FIG. 2. In contrast to this, as can be understood from FIG. 8, the separation distance between the article to be sewn 100 and the post bed 60 becomes greater as the post bed 60 approaches the bent portion 124.

The separation distance between the article to be sewn 100 and the post bed 60 is approximately equal to the length of the portions of the threads 74 a and 74 b from the first sewing needle 72 a and the second sewing needle 72 b to the first looper 62 a and the second looper 62 b (also referred to below as the “needle-to-looper portion”). In other words, the length of the needle-to-looper portion is smallest when sewing at the flat portion, and becomes gradually larger as the first sewing needle 72 a, the second sewing needle 72 b, and the post bed 60 approach the bent portion 124 from the flat portion. Furthermore, the length of the needle-to-looper portion is largest when sewing at the bent portion 124.

In this way, when the sewing transitions from the flat portion to the bent portion 124, a difference occurs in the separation distance between the article to be sewn 100 and the post bed 60. Specifically, compared to a case of sewing at the flat portion, the separation distance between the article to be sewn 100 and the post bed 60 becomes greater. As a result, the length of the needle-to-looper portions of the threads 74 a and 74 b increases.

After this, the first sewing needle 72 a, the second sewing needle 72 b, and the post bed 60 pass by the bent portion 124 and descend to arrive at the flat portion. At this time, the length of the needle-to-looper portion becomes gradually smaller as the distance from the bent portion 124 increases. In accordance with this, the length of the needle-to-looper portions of the threads 74 a and 74 b becomes smaller. Based on this, the threads 74 a and 74 b become loose. This looseness occurs easily particularly when the article to be sewn 100 is not being pressed by a presser foot or the like. When looseness occurs, this causes stitching defects such as fraying. Furthermore, in certain situations, the first sewing needle 72 a and the second sewing needle 72 b can become unable to pass through the loop portions 110.

In order to avoid this, the control section 90 temporarily stops the sewing robot 16 when, for example, the first sewing needle 72 a, the second sewing needle 72 b, and the post bed 60 pass by the bent portion 124 and come to the flat portion so that the length of the needle-to-looper portion differs (becomes shorter, in this case) by at least a prescribed amount from the length of the needle-to-looper portion up to this point. Further, the control section 90 activates the thread pushing air cylinder 80 in a state where the sewing motor 54 has been stopped. In other words, the thread pushing rod 84 is caused to move forward.

As described above, the threads 74 a and 74 b are passed through the thread passing groove 82 formed in the thread pushing air cylinder 80. Therefore, when the thread pushing rod 84 moves forward, the portions of the threads 74 a and 74 b on the tip side of the thread pushing rod 84 are pulled by the thread pushing rod 84, as shown in FIG. 9. As a result, the tip sides of the threads 74 a and 74 b are pulled in the direction away from the post bed 60, that is, toward the thread supplying section side.

Due to this pulling, the looseness of the threads 74 a and 74 b is eliminated. In other words, the threads 74 a and 74 b are tensed. In this state, the control section 90 reactivates the sewing robot 16 and the sewing motor 54. In other words, the sewing is resumed and the threads 74 a and 74 b are fed to the flat portion of the article to be sewn 100.

The threads 74 a and 74 b are already tense, as described above. Therefore, the occurrence of fraying is effectively avoided. Furthermore, the first sewing needle 72 a and the second sewing needle 72 b easily pass through the loop portions 110. As a result, it is possible to form aesthetically beautiful parallel stitches 112 even in the flat portion on the downstream side of the bent portion 124 in the sewing direction.

When the control section 90 detects that the parallel stitches 112 with a prescribed length have been formed, the operation of the sewing robot 16 is stopped under the control of the control section 90, and the sewing motor 54 is deactivated. Accordingly, the back and forth movement of the first sewing needle 72 a and the second sewing needle 72 b and the rotation of the first looper 62 a and the second looper 62 b are stopped. After regions of the threads 74 a and 74 b between the article to be sewn 100 and the first sewing needle 72 a and the second sewing needle 72 b have been cut, the sewing robot 16 operates suitably to move the sewing mechanism 14 away from the article to be sewn 100. Thus, the sewing is ended.

As described above, when the sewing transitions from the flat portion to the bent portion 124, the separation distance between the article to be sewn 100 and the post bed 60, and therefore the length of the needle-to-looper portions of the threads 74 a and 74 b, become larger. When sewing is performed on the bent portion 124 in this state, the threads 74 a and 74 b are pulled, and can bite into the article to be sewn 100.

Therefore, a second thread pulling mechanism may be provided to pull the threads 74 a and 74 b in a direction toward the post bed 60. In this case, when the article to be sewn 100 and the post bed 60 are separated during sewing by at least a prescribed amount compared to the sewing up to this point (the immediately preceding sewing), the threads 74 a and 74 b may be pulled in the direction toward the post bed 60 by the second thread pulling mechanism. In accordance with this, the threads 74 a and 74 b are pulled by a small amount from the thread supplying section, and therefore the tension of the threads 74 a and 74 b is eliminated. As a result, the threads 74 a and 74 b are prevented from biting into the article to be sewn 100.

The present invention is not limited to the above-described embodiment, and various modifications can be adopted therein without departing from the essence and gist of the present invention.

For example, instead of the thread pushing air cylinder 80, a rotary actuator 130 (winding mechanism) shown in FIG. 10 may be provided as a component serving as both the thread supplying section and the thread pulling mechanism. In this case, after the threads 74 a and 74 b have been loosened, a rotating cylinder 132 forming the rotary actuator 130 rotates by a prescribed rotational angle. Due to this rotation, the threads 74 a and 74 b are wound on the rotating cylinder 132 and tensed, and therefore it is possible for the threads 74 a and 74 b to pass through the loop portions 110 in the same manner as described above. In other words, with this configuration as well, it is possible to realize aesthetically beautiful parallel stitches 112.

Furthermore, the number of sewing machine needles and the number of loopers may be one.

Furthermore, the article to be sewn 100 is not limited to being the interior base material 102 and the skin material 104 of the instrument panel for an automobile, and may be any article that can be pierced by a sewing machine needle.

Yet further, the seating portions 24 may be formed using suction pads. 

What is claim is:
 1. A sewing method for forming stitches on an article to be sewn, using a needle configured to pierce or withdraw from the article to be sewn in accordance with repetition of back and forth movement, and a looper that faces the needle with the article to be sewn therebetween and is housed inside a post bed, the sewing method comprising when the post bed has become closer to the article to be sewn by at least a prescribed amount than in immediately preceding sewing, pulling a thread hooked on the needle in a direction away from the post bed, or, when the post bed has become farther from the article to be sewn by at least a prescribed amount than in the immediately preceding sewing, pulling the thread hooked on the needle in a direction toward the post bed.
 2. A sewing device that forms stitches on an article to be sewn, using a needle configured to pierce or withdraw from the article to be sewn in accordance with repetition of back and forth movement, and a looper that faces the needle with the article to be sewn therebetween and is housed inside a post bed, the sewing device comprising: a thread pulling mechanism configured to pull a thread , which has been hooked on the needle, in a direction away from or toward the post bed; and a control section configured to perform control to operate the thread pulling mechanism when a distance between the post bed and the article to be sewn differs by at least a prescribed amount from a distance in immediately preceding sewing.
 3. The sewing device according to claim 2, wherein: the thread pulling mechanism is a pushing device configured to push the thread.
 4. The sewing device according to claim 3, wherein the pushing device is formed from a cylinder device including a rod, and pushes the thread with the rod.
 5. The sewing device according to claim 2, wherein the thread pulling mechanism is a winding device configured to wind the thread.
 6. The sewing device according to claim 5, wherein the winding device also functions as a thread supplying section configured to supply the thread.
 7. The sewing device according to claim 5, wherein the winding device is formed from a rotary actuator including a rotating cylinder, and the thread is wound on the rotating cylinder. 